An active photovoltaic (“PV”) solar cell usually has metallic conductor lines on its front, sun-facing, surface. These conductor lines are essential to the operation of the electrical circuit of which the PV solar cell is a part. However, at the same time, these front side metallic conductor lines block a portion of the incident solar radiation from entering the active semiconductor materials in the solar cell. Thus, the obscured radiation is not able to contribute to the photovoltaic current produced by the cell.
The losses in photovoltaic conversion efficiency due to the presence of front side conductor lines are found in many different types of photovoltaic arrangements, from flat panel PV modules to PV modules designed for use at 1 kW/m2 irradiance (approximately the irradiance of the sun at the surface of the earth) to concentrating photovoltaic (“CPV”) modules in which the solar radiation is concentrated to 5, 50, or even greater than 500 times the irradiance of the sun and focused on higher efficiency PV solar cells.
Accordingly, it is believed to be advantageous to provide an article in the form of an optical element usable in combination with a photovoltaic solar cell to form a photovoltaic cell assembly in which radiation incident on the optical element is directed away from the front side conductor lines and towards the active semiconductor materials of the PV cell, so that substantially all of the radiation, regardless of incident angle, contributes to the output of the photovoltaic cell assembly and of the module and system of which it is a part.
The radiation durability of such an optical element is also a critical consideration. Radiation durability refers to the ability of a material from which the optical element is made to withstand a predetermined level of irradiance for the desired lifetime of the article. Thus, a flat panel PV module (i.e., a module designed for use at 1 kW/m2 irradiance) must be able to withstand an irradiance of 1 KW/m2 of solar radiation for the desired lifetime (typically twenty-five years) of the PV module and any system in which it is used.
In the case of CPV modules the radiation durability requirements are more stringent since for an identical lifetime the irradiance level is much higher, and the total dose of solar radiation into the materials in concomitantly larger, by a concentration factor.
Accordingly, is it believed to be of further advantage that an optical element that serves to enhance light collection efficiency of a photovoltaic solar cell is, at the same time, also radiation durable for the application and lifetime for which it is used.